Mold core assembly and investment casting method

ABSTRACT

The present invention discloses a mold core assembly. The mold core assembly includes at least one core. The core comprises a main body member and a high temperature-resistant material with a melting point over 1500° C., the length-diameter ratio of the main body member is greater than 50, and the main body member includes a high melting point metal with a melting point over 1500° C. The mold core assembly also includes a shell mold, wherein the shell mold encloses the core to form a cavity between the shell mold and the core, so as to accommodate a molten casting metal. The present invention further discloses an investment casting method.

TECHNICAL FIELD

The present invention relates to a mold core assembly and an investment casting method and in particular, to a mold core assembly and an investment casting method for casting a casting provided with a long deep hole and a core.

BACKGROUND

An investment casting method is widely used to mold a metal component with a complex geometric structure, especially, a component provided with an internal hole. In the investment casting method, a mold core assembly is first molded. The mold core assembly includes a shell mold and a core fastened in the shell mold; then molten steel is poured into the molded mold core assembly, to form a solid metal casting after cooling. After the casting is finished, the shell mold and the core are removed. The existing core is made of a ceramic material. The ceramic is high temperature-resistant but brittle and is subject to fracture. Especially, when a relatively large component provided with a relatively long hole is casted, a ceramic core is also relatively long. Consequently, the ceramic core is more likely subject to fracture due to low strength of the ceramic core.

Therefore, it is necessary to provide a solution to resolve the at least one problem mentioned above.

BRIEF DESCRIPTION

One aspect of the present invention provides a mold core assembly. The mold core assembly includes: at least one core, where the core includes a main body member and includes a high temperature-resistant material with a melting point over 1500° C., a length-diameter ratio of the main body member is greater than 50, and the main body member includes a high melting point metal with a melting point over 1500° C.; and a shell mold, where the shell mold encloses the core to form a cavity between the shell mold and the core, so as to accommodate a molten casting metal.

Another aspect of the present invention provides an investment casting method. The investment casting method includes: forming at least one core, where the core includes a main body member and includes a high temperature-resistant material with a melting point over 1500° C., a length-diameter ratio of the main body member is greater than 50, and the main body member includes a high melting point metal with a melting point over 1500° C.; forming a shell mold, where the shell mold encloses the core to form a cavity between the shell mold and the core; flowing a molten casting metal into the cavity to form a casting; and removing the shell mold.

BRIEF DESCRIPTION OF THE DRAWINGS

To understand the present invention better, implementation manners of the present invention are described with reference to the accompanying drawings. In the accompanying drawings:

FIG. 1 shows a sectional view of a mold core assembly according to an embodiment of the present invention;

FIG. 2 shows a sectional view of a mold core assembly according to another embodiment of the present invention;

FIG. 3 shows a sectional view of a mold core assembly according to another embodiment of the present invention;

FIG. 4 shows a sectional view of a mold core assembly according to another embodiment of the present invention;

FIG. 5 shows a sectional view of a mold core assembly according to another embodiment of the present invention;

FIG. 6 shows a sectional view of a mold core assembly according to another embodiment of the present invention;

FIG. 7 shows a sectional view of a mold core assembly according to another embodiment of the present invention;

FIG. 8 shows a sectional view of a mold core assembly according to another embodiment of the present invention;

FIG. 9 shows a schematic sectional diagram of a mold core assembly according to another embodiment of the present invention;

FIG. 10 shows a sectional view of a mold core assembly according to another embodiment of the present invention; and

FIG. 11 shows a flowchart of an investment casting method according to an embodiment of the present invention.

DETAILED DESCRIPTION

Unless otherwise defined, the technical terms or scientific terms used herein shall be the ordinary meaning understood by a person having ordinary skill in the technical field of the present invention. “First”, “second”, and similar words used in the patent application specification and claims of the present invention do not denote any order, quantity, or importance, and are simply used to distinguish different components. Similarly, “one”, “a/an”, or the similar terms also do not impose any limitations on quantity, but indicate at least one. In addition, “connected to”, “connected with”, or the similar expressions are not used to differentiate whether two components are connected directly or indirectly. Certainly, components may be directly or indirectly connected, unless otherwise specified.

A mold core assembly in the present invention can be configured for investment casting. The mold core assembly can be configured to cast a turbine component by means of investment casting, for example, blades of various shapes and sizes, where a relatively deep inner bore can be provided inside a blade. The mold core assembly can be configured to cast a cooling pipe of an exhaust cylinder, or can be configured to cast another component, where a relatively long hole may be provided inside the casted component. FIG. 1 shows a sectional view of a mold core assembly 10 according to an embodiment. The mold core assembly 10 includes at least one core 12 and a shell mold 14. For a purpose of illustration, only one core 12 is shown in the figure. In actual application, the mold core assembly 10 may have one or more cores 12. The quantity of the cores 12 may be determined according to the quantity of holes as required in actual application.

The core 12 includes a main body member 16 and includes a high temperature-resistant material with a melting point over 1500° C. A length-diameter ratio of the main body member 16 is greater than 50. In this embodiment, the main body member 16 is a cylindrical solid rod. The length-diameter ratio of the main body member 16 is of a longitudinal length L to a diameter D of a cross section that are of the main body member 16. For example, the longitudinal length L of the main body member is 300 mm, and the diameter of the cross section is 2 mm. This is merely an example, and is not limited thereto. In addition, the length-diameter ratio of the main body member 16 is not limited to a proportional relationship denoted in the figure. The main body member 16 includes a high melting point metal with a melting point over 1500 C. In this embodiment, the main body member 16 further includes the high temperature-resistant material. The high melting point metal and the high temperature-resistant material are mixed together. The main body member 16 includes a base 18 and an additive 20 mixed in the base 18. In an embodiment, the base 18 includes the high melting point metal, and the additive 20 includes the high temperature-resistant material. In another embodiment, the base 18 includes the high temperature-resistant material, and the additive 20 includes the high melting point metal. In the embodiment shown in the figure, the additive 20 is in a powder form, and distributed in the base 18. In another embodiment, the main body member 16 includes a cermet. The cermet includes the high melting point metal and a ceramic. The ceramic is a high temperature-resistant material.

In an embodiment, a high temperature-resistant material includes at least one of the following types: quartz, ceramic, platinum-group metal, or a cermet. The high temperature-resistant material may be a pure metal, an alloy, or a composite of the metal described above. The cermet is a structural material combing a hard phase ceramic with a metal or a binder phase alloy, and has good toughness and thermal stability. In an embodiment, the cermet includes a WC—Co composite material or a TiC—TiN—Mo—Ni composite material. In an embodiment, the high melting point metal includes at least one of the following types: molybdenum, tungsten, titanium, platinum-group metal, tantalum, chromium, or a niobium. The main body member 16 may include a pure metal, an alloy, or a composite of the high melting point metal described above. In an embodiment, the main body member 16 may include a molybdenum-based alloy, such as a Mo—Cr (MoCr) alloy, a Mo—Co—Cr (MoCoCr) alloy, a Mo—W alloy (MoW), or a Mo—Zr—Ti (TZM, MoZrTi) alloy. The main body member 16 may include a W-based alloy (W based alloy) or a Ti—Mo (TiMo) alloy.

Different materials are selected from the high temperature-resistant material and the high melting point metal to form the core 12. Therefore, the core 12 includes at least two different materials. The high temperature-resistant material can prevent the core 12 from distortion resulting from high temperature of a molten casting metal (such as a nickel-based super alloy or a cobalt-based super alloy). The metal material can improve strength and/or toughness of the core 12. In this embodiment, the melting point of the high melting point metal is higher than a melting point of the casting metal. The high melting point metal is not subject to melting in the high temperature of the molten casting metal.

The shell mold 14 encloses the core 12, to form a cavity 22 between the shell mold 14 and the core 12, so as to accommodate the molten casting metal (not shown in the figure). The shell mold 14 may be made of a ceramic material. A shape and a size of the shell mold 14 are the same as those of a desired component. A location of the core 12 in the shell mold 14 is determined according to that of a hole of the desired component. After the casting is finished, the core 12 in this embodiment can be completely removed by means of erosion.

FIG. 2 shows a sectional view of a mold core assembly 10 according to another embodiment. The mold core assembly 10 shown in FIG. 2 is similar to the mold core assembly 10 shown in FIG. 1. Compared with the mold core assembly 10 shown in FIG. 1, a core 12 of a main body member 16 of the mold core assembly 10 shown in FIG. 2 is a hollow tube. A length-diameter ratio of the main body member 16 is a ratio of a length L and an external diameter D of the hollow tube. A size of the external diameter D of the hollow tube is the same as that of a diameter of a desired hole. A material of the main body member 16 shown in FIG. 2 is similar to that of the main body member 16 shown in FIG. 1. After the casting is finished, the core 12 in this embodiment is completely removed. When the core is removed by means of erosion, an exposed area of the hollow tube is relatively large, and an area in contact with an erosive fluid is relatively large. Therefore, it is relatively easy to remove the hollow tube.

FIG. 3 shows a sectional view of a mold core assembly 10 according to another embodiment. The mold core assembly 10 shown in FIG. 3 is similar to the mold core assembly 10 shown in FIG. 1. A core 12 of the main body member 16 shown in FIG. 3 includes a base 18 and an additive 20 mixed in the base 18. Compared with the embodiment shown in FIG. 1, the additive 20 in FIG. 3 is a thin filament. The thin filament is routed along a longitudinal direction of the core 12 in the base 18. In another embodiment, the filamentous additive 20 may be routed in the base 18 in an interleaved manner. In still another embodiment, the additive 20 may be in another shape. In the embodiment shown in FIG. 3, the core 12 is a spindly solid rod. In another embodiment, as shown in FIG. 4, a core 12 is a hollow tube, with a shape similar to that of the core 12 shown in FIG. 2. The core 12 in FIG. 4 is made of a material same as that of the core 12 shown in FIG. 3. This is not described herein again. After the casting is finished, the cores 12 in the embodiments of FIG. 3 and FIG. 4 are completely removed.

FIG. 5 shows a sectional view of a mold core assembly 10 according to another embodiment. The mold core assembly 10 shown in FIG. 5 is similar to the mold core assembly 10 shown in FIG. 1. Compared with the mold core assembly 10 shown in FIG. 1, a core 12 of the mold core assembly 10 shown in FIG. 5 further includes a coating layer 24 formed on an external surface of a main body member 16. The coating layer 24 includes a high temperature-resistant material. In this embodiment, the main body member 16 is made of a high melting point metal. The coating layer 24 can prevent the main body member 16 from distortion resulting from high temperature of a molten casting metal, and prevent reaction between the high melting point metal of the main body member 16 and the molten casting metal, and prevent surface oxidation of the main body member 16. In an embodiment, the coating layer 24 is a thin layer applying the high temperature-resistant material to the main body member 16. In another embodiment, the coating layer 24 may be a granular high temperature-resistant material distributed on the surface of the main body member 16. In another embodiment, the main body member 16 is a base made of the high melting point metal mixed with the high temperature-resistant material. The high temperature-resistant material of which the main body member 16 is made may be the same as or different from the high temperature-resistant material of the coating layer 24. After the casting is finished, the core 12 in this embodiment is completely removed.

FIG. 6 shows a sectional view of a mold core assembly 10 according to another embodiment. The mold core assembly 10 shown in FIG. 6 is similar to the mold core assembly 10 shown in FIG. 5. Compared with the mold core assembly 10 shown in FIG. 5, a main body member 16 of a core 12 of the mold core assembly 10 shown in FIG. 6 is a hollow tube. In an embodiment, an external surface of the hollow tube 16 is coated with a coating layer 24. In another embodiment, both an external surface and an internal surface of the hollow tube 16 are coated with the coating layer 24. Materials of the coating layer 24 and the main body member 16 in this embodiment are similar to those in the embodiment shown in FIG. 5.

FIG. 7 shows a sectional view of a mold core assembly 10 according to another embodiment. A main body member 16 of a core 12 in FIG. 7 is a hollow tube. The hollow tube 16 includes a high melting point metal material. The core 12 further includes filling material 26 into which the hollow tube 16 is filled. The filling material 26 is a high temperature-resistant material. The high temperature-resistant filling material 26 can be used to cool the hollow tube 16, so as to prevent the hollow tube 16 from distortion resulting from high temperature casting. In this embodiment, the filling material 26 includes powder, for example, ceramic powder. The ceramic powder can be injected into the hollow tube 16 by virtue of fluidity, and can be poured out from the hollow tube 16 after casting is finished. In an embodiment, the hollow tube 16 is a melt-resistant metal in a molten casting metal. After casting is finished, the hollow tube 16 is removed. In another embodiment, the hollow tube 16 is made of a high melting point metal material similar to or the same as a casting metal, such as a nickel-based super alloy or a cobalt-based super alloy. A melting point of the high melting point metal of the hollow tube 16 is approximate to or the same as that of the casting metal. In an embodiment, a high melting point metal material of the hollow tube 16 may be a nickel-based super alloy GTD111, GTD222 or GTD444 of the General Electric Company. GTD111, GTD222, and GTD444 all contain a nickel (Ni) by over 50%, of some chromium (Cr), a small amount of other metal elements (such as cobalt (Co), tungsten (W), and aluminum (Al)), and a small amount of non-metal elements (such as carbon (C), and boron (B)). The high melting point metal material of the hollow tube 16 may be a nickel-based super alloy IN738. The nickel-based super alloy IN738 contains 62 weight percent (wt. %) nickel, 16 wt. % chromium, and a small amount of metal elements and non-metal elements. The material of the hollow tube 16 is not limited to the materials mentioned above. After the casting is finished, the hollow tube 16 is left in the casting, and is served as a desired component together with the casting. In this case, an internal size of the hollow tube 16, for example, an internal diameter, is set to be the same as that of a desired hole. In this way, an interior chamber wall of the hole is relatively smooth.

FIG. 8 shows a sectional view of a mold core assembly 10 according to an embodiment. The mold core assembly 10 shown in FIG. 8 is similar to the mold core assembly 10 shown in FIG. 7. Compared with the mold core assembly 10 shown in FIG. 1, in FIG. 8, a filling material 26 includes a solid rod in contact with a hollow tube 16. The filling material 26 is a rod-like high temperature-resistant material and is in complete contact with the hollow tube 16. In another embodiment, the filling material 26 may be in another shape. The filling materials 26 in FIG. 7 and FIG. 8 may be used to fill into the hollow tubes in FIG. 2, FIG. 4 and FIG. 6.

FIG. 9 shows a schematic sectional diagram of a mold core assembly 10 according to another embodiment. FIG. 9 shows cross sections of main body members 161 and 162 of two types of cores. The main body member 161 has a circular cross section. The main body member 162 has a non-circular cross section. In this embodiment, the cross section is oval. If the cross section of the main body member 162 is oval, a length-diameter ratio of the main body member 162 is a ratio of a longitudinal length to a longer diameter of the main body member 162. In another embodiment, the main body member 16 may have another shape of non-circular cross section, such as a rectangle, a polygon, or an irregular shape (not shown in the figure). In this case, the length-diameter ratio of the main body member 16 is a ratio of a longitudinal length to a longest radial length of a cross section that are of the main body member 16. In an embodiment, the main body member 16 has different cross sections.

FIG. 10 shows a sectional view of a mold core assembly 10 according to an embodiment. In this embodiment, a main body member 16 of a core 12 does not have a straight shape. The main body member 16 is not straight longitudinally. In an embodiment, the main body member 16 is arched longitudinally. In another embodiment, the main body member 16 has a regular or irregular un-straight shape longitudinally. A length-diameter ratio of the main body member 16 is a ratio of a total length of a longitudinal curve to a longest radical length. The main body member 16 in FIG. 10 may be a hollow tube or a solid rod. A structure and a material of the core 12 are similar to those in embodiments shown in FIGS. 1 to 9.

The cores in the embodiments shown in FIG. 1 to FIG. 10 are made of metal with a high melting point. The cores 12 are not subject to fracture by virtue of good strength and toughness. The cores 12 further include a high temperature-resistant material, so as to prevent the cores 12 from distortion and oxidation. In this way, a relatively long core 12 whose length-diameter ratio is greater than 50 can be manufactured, so as to form a relatively long hole. In addition, a relatively long and complex core 12 can be manufactured, so as to form a hole with a complex shape.

FIG. 11 shows a flowchart of an investment casting method 40 according to an embodiment. Step 41. Form at least one core. The core includes a main body member and includes a high temperature-resistant material with a melting point over 1500° C. A length-diameter ratio of the main body member is greater than 50, and the main body member includes a high melting point metal with a melting point over 1500° C. In an embodiment, the main body member is produced at least by using the high melting point metal and the high temperature-resistant material. A main body member with a solid rod or a main body member with a hollow tube can be formed. In an embodiment, the main body member includes a base and an additive mixed in the base. The base includes the high melting point metal, and the additive includes the high temperature-resistant material. In another embodiment, the base includes the high temperature-resistant material, and the additive includes the high melting point metal. In an embodiment, a coating layer is coated on an external surface of the main body member. The coating layer includes a high temperature-resistant material. In another embodiment, the main body member is a hollow tube. A filling material is filled into the hollow tube. The filling material includes the high temperature-resistant material. The filling material may be powder or a solid rod. The cores described in the embodiments shown in FIG. 1 to FIG. 10 may be obtained by performing the step 41 of forming a core. Descriptions are not made repeatedly herein again.

Step 43. Form a shell mold. The shell mold encloses the core, to form a cavity between the shell mold and the core. In an embodiment, a desired molding component is casted by using a mold molding material (such as wax). Next, a shell mold that envelopes a mold is formed outside of the mold. Then, the mold molding material is removed to left the shell mold. In this way, a shape and a size of the shell mold are the same as those of the component. In an embodiment, the core is embedded in the mold molding material. After the mold molding material is removed, the core is left in the shell mold. In another embodiment, after the shell mold is formed, the core is placed into the shell mold and fastened. The shell mold may be made of ceramic slurry. In this way, a mold core assembly is formed. The cavity between the shell mold and the core is formed, so as to accommodate a molten casting metal.

Step 45. Flow a molten casting metal into a cavity to form a casting. A high temperature molten casting metal is poured into the shell mold, and forms a solidified casting followed by rapid cooling. Step 47. Remove the shell mold. In an embodiment, a ceramic shell mold is removed by means of erosion. In an embodiment, the main body member of the core is manufactured by a metal similar to the casting metal. In addition, when an external surface of the main body member is not provided with a coating layer made of a high temperature-resistant material, the main body member of the core may be left in the casting, and is served as a desired component together with the casting. The main body member is a hollow tube. A high temperature-resistant filling material into which the hollow tube is filled is used to cool the hollow tube. After the casting is finished, the filling material is removed. An internal size of the hollow tube is equal to that of a desired hole. In another embodiment, the casting method 40 further includes: removing the core completely. The core can be completely removed by means of erosion; for example, when the main body member of the core includes a high temperature-resistant material, or the core has a coating layer made of the high temperature-resistant material, or the high melting point metal material of the core is different from or not similar to the casting metal, the core is completely removed. An external size of the core is consistent with that of the desired hole.

Operations of the method 40 are shown in a form of functional modules. A sequence of modules shown in FIG. 11 and division of operation modules are not limited to the embodiment shown in the figure; for example, some modules may be performed in a different sequence. An operation in one module may be combined with operations in another or multiple modules, or divided into multiple modules.

Although the present invention is described with reference to the specific implementation manners, a person skilled in the art can understand that modifications and variations of the present invention can be made. Therefore, it can be learned that the claims are intended to include all modifications and variations within the concept and protection scope of the present invention. 

What is claimed is:
 1. A mold-core assembly, comprising: at least one core comprising a main body with an aspect ratio of larger than 50 and comprising a high temperature resistant material with a melting point of higher than 1500 degree Celsius, the main body comprising a metal with a melting point of higher than 1500 degree Celsius; and a shell mold surrounding the at least one core and spaced away from the at least one core to define a cavity for receiving molten base metal.
 2. The mold-core assembly of claim 1, wherein the main body comprises a matrix and a plurality of additives therein, the matrix comprises the metal and the plurality of additives comprise the high temperature resistant material.
 3. The mold-core assembly of claim 1, wherein the main body comprises a matrix and a plurality of additives therein, the matrix comprises the high temperature resistant material and the plurality of additives comprise the metal.
 4. The mold-core assembly of claim 1, wherein the at least one core further comprises a coating formed outside of the main body and comprising the high temperature resistant material.
 5. The mold-core assembly of claim 1, wherein the high temperature resistant material comprises at least one of quartz, ceramic, platinum group metals and cermet.
 6. The mold-core assembly of claim 1, wherein the main body comprises a tube comprising the metal, the at least one core further comprises a filler inside the tube, and the filler comprises the high temperature resistant material.
 7. The mold-core assembly of claim 6, wherein the filler comprises a plurality of powders filling in the tube.
 8. The mold-core assembly of claim 6, wherein the filler comprises a solid rod filling in and attached to the tube.
 9. The mold-core assembly of claim 1, wherein the metal of the main body comprises at least one of molybdenum, tungsten, titanium, platinum group metals, tantalum, chromium and niobium.
 10. The mold-core assembly of claim 1, wherein the main body of the at least one core comprises a cermet comprising the metal and a ceramic.
 11. The mold-core assembly of claim 1, wherein the main body comprises a non-round cross-section.
 12. The mold-core assembly of claim 1, wherein the main body comprises a non-straight shape.
 13. A method, comprising: forming at least one core comprising a main body with an aspect ratio of larger than 50 and comprising a high temperature resistant material with a melting point of higher than 1500 degree Celsius, the main body comprising a metal with a melting point of higher than 1500 degree Celsius; forming a shell mold surrounding the at least one core and spaced away from the at least one core to define a cavity; introducing molten base metal to the cavity to form a cast body; and removing the shell mold.
 14. The method of claim 13, wherein the main body comprises a matrix and a plurality of additives therein, the matrix comprises the metal and the plurality of additives comprise the high temperature resistant material.
 15. The method of claim 13, wherein the main body comprises a matrix and a plurality of additives therein, the matrix comprises the high temperature resistant material and the plurality of additives comprise the metal.
 16. The method of claim 13, wherein forming the at least one core further comprises forming a coating outside of the main body, and the coating comprises the high temperature resistant material.
 17. The method of claim 13, wherein the main body comprises a tube comprising the metal, and forming the at least one core further comprising filling the tube with a filler comprising the high temperature resistant material.
 18. The method of claim 13, wherein the metal of the main body comprises at least one of molybdenum, tungsten, titanium, platinum group metals, tantalum, chromium and niobium.
 19. The method of claim 13, wherein the high temperature resistant material comprises at least one of quartz, ceramic, platinum group metals and cermet.
 20. The method of claim 13, wherein the main body of the at least one core comprises a cermet comprising the metal and a ceramic. 